( nland approximately half the snails on...)Parasites' impact goes beyond host to affect ecosystem

nland, approximately half the snails on Appledore Island are infected. That’s because L. littorea is just one of three hosts in the life cycle of C. lingua, which first lives in the snails?gonads then moves to a fish as its second host. Shorebirds ?more prevalent on Appledore than on the mainland ?are the final hosts, contracting infection by eating infected fish, then in their feces excreting the eggs of C. lingua, which are in turn eaten by the snails.

"The parasite’s life cycle is a really amazing strategy for an organism that doesn’t have a brain," says Byers, who predicts that anywhere gulls are prevalent, the C. lingua trematode would also be prevalent.

A laboratory experiment confirmed Wood’s and Byers?hypothesis: snails infected with the parasite ate 40 percent less macroalgae than uninfected snails. In the field, where researchers measured the macroalgae in three types of bottomless cages -- with no snails (control), uninfected snails, and infected snails -- they similarly saw less reduction of ephemeral algae by infected snails.

But when researchers isolated ephemeral, or edible, algae, "we saw dramatic change," says Byers. Edible algae account for a small proportion of macroalgae on rocky shorelines ?just about seven percent ?but they are an important food and habitat resource for a variety of organisms. Over the three-and-a-half-week field experiment, ephemeral algae increased 186 percent in the no-snails control cage and 59 percent in the cage of infected snails; it decreased by six percent in the uninfected snails treatment.

"Whatever controls that edible algae controls a lot," says Byers, noting that other snails, isopods, and possibly near-shore fish feed on ephemeral algae. "It’s suggestive that these non-lethal impacts of parasites have influential effects that can trickle down to affect other residents of the ecosystem."

Byers?and Wood’s study signals an increasing appreciation for parasites in e
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Source:University of New Hampshire

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